In this thesis, an experimental and theoretical study of two and three vector correlations in the inelastic scattering of NO(X) with various rare gas atoms is presented. Vector correlations for a selection of rare gas systems were determined experimentally, and the observations were interpreted using a variety of classical and quantum mechanical models. The experiment is able to provide state-to-state resolution of the dynamics by means of an electrostatic hexapole and 1+1' resonantly enhanced multi-photon ionisation (REMPI). The simplest vector correlation of interest is the differential cross section (DCS), given by the <b>k</b>-<b>k</b>' correlation. The DCSs were determined experimentally for the NO(X)--Kr and NO(X)--Xe collision systems, both characterised by the relatively deep (&asymp;140cm^-1) attractive well and large extent of the attractive potential. The agreement between the experimental angular distributions and quantum mechanical DCS is very good for both systems. Classical calculations fail to correctly reproduce the form and magnitude of the DCS for either system, reflecting the inherently quantum mechanical nature of the collision. The classical calculations do however provide mechanistic insight into regions where the attractive part of the potential plays an important role in determining the dynamics. In order to investigate narrow angular features in the forward scattered direction, several experimental improvements to molecular beams and the detection ion-optic stack were made. Investigation into these structures revealed a strong contribution from molecular diffraction into the classical shadow of the NO(X), and the simple Fraunhofer model revealed a preference for scattering from an individual m&rarr;m' sub-state. Such measurements are in a region of the DCS where scattering is forbidden classically, and reveal the purely quantum nature of the collision interaction in the forward scattered direction. The low order <b>k</b>-<b>k</b>' correlation was then extended by using linearly or circularly polarised laser excitation. The interaction of the light with the molecular dipole allows the measurement of the <b>k</b>-<b>k</b>'-<b>j</b>' correlation. When linearly polarised light was used for the excitation laser, two of the rank two p^{2}_q(&theta;) renormalised polarisation dependent differential cross sections (PDDCSs), which describe rotational alignment, were obtained. With circularly polarised light, the rank one p^{1}_1-(&theta;) renormalised PDDCSs describing rotational orientation were determined. The collision induced alignment in NO(X)--Xe scattering was found to be well reproduced by classical and impulsive theories, highlighting the fact that the alignment is dominated by the propensity for the projection of <b>j</b> onto the kinematic apse to be conserved. The attractive part of the potential does augment the alignment renormalised PDDCSs, and this is most evident in states with strong features of the attractive part of the potential such as ℓ-type rainbows. The orientation is more strongly influenced by the attractive part of the potential and is also influenced by parity. In addition to the parity effect, there exist two limiting classical mechanisms which govern the orientation, one caused by attraction and the other repulsion. Finally, the bond axis of the NO(X) can be oriented by means of hexapole state selection combined with adiabatic orientation using a set of guiding rods. The integral steric effect, an <b>r</b>-<b>k</b> correlation, was measured for the NO(X)--Kr and NO(X)--Ar spin-orbit changing systems. There are large oscillations in the sign of the steric asymmetry which occur for scattering with the various rare gases. There are also large differences between the rare gases as the potentials become more attractive, and more isotropic. The steric asymmetry is well reproduced by quantum mechanics, however, a classical mechanism becomes dominant at high &Delta;j.

Submitted by Irene Nascimento (irene.kessia@ufpe.br) on 2016-09-28T19:19:22Z No. of bitstreams: 2 license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) Dissertação PPGEM - Francisco Alves de Lima Júnior.pdf: 7760423 bytes, checksum: b0d747f5e3c3795b57483f19b676a178 (MD5) / Made available in DSpace on 2016-09-28T19:19:22Z (GMT). No. of bitstreams: 2 license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) Dissertação PPGEM - Francisco Alves de Lima Júnior.pdf: 7760423 bytes, checksum: b0d747f5e3c3795b57483f19b676a178 (MD5) Previous issue date: 2016-02-03 / A pesquisa que deu origem a esta dissertação foi realizada a partir de dados de propriedades mecânicas obtidos de testes e ensaios de inspeção, performance e controle de qualidade, executados em tubos fabricados em material polimérico, com e sem orientação molecular. Foram eles: Resistência ao Impacto, Resistência à Pressão Hidrostática Interna, Grau de Gelificação e Resistência ao Cloreto de Metileno, Resistência à Compressão Diametral, Estabilidade Dimensional, Classe de Rigidez e Resistência ao Achatamento, Resistência o Prolongamento da Fissura e Grau de Orientação Molecular. Para obtenção dos dados, os materiais foram testados em condições reais e extremas de operação, em sistemas, equipamentos, instrumentos, “softwares” e acessórios especificados, montados e calibrados em laboratório e instalações fabris, conforme normativos técnicos. Para registros dos dados foram utilizados sistemas informatizados acessórios aos equipamentos, assim como planilhas eletrônicas e “softwares” de controle estatístico e descritivo e para parametrização de ensaios mecânicos. Os dados e resultados foram analisados segundo parâmetros e critérios de estabilidade dimensional, tenacidade e rigidez, resistência à pressão hidrostática interna, ao impacto, ao cloreto de metileno, à compressão diametral e ao prolongamento de fissura, associados ao seu grau de orientação molecular, baseados em bibliografias e normas técnicas referentes às análises, ensaios e materiais empregados. Estes critérios abrangem o dimensionamento, cálculo e comparação de parâmetros, quando do material aplicado ao projeto de tubos. Foram avaliados os efeitos resultantes da orientação molecular nas propriedades mecânicas finais dos produtos acabados. Foi observado que o processo de orientação molecular proporcionou ao material maior tenacidade, maior resistência à transmissão da fissura, bem como maiores resistências a fadiga, impacto, tração, compressão e deformação, maior módulo de elasticidade, e consequente diminuição de coeficientes de segurança aplicados ao projeto. / The research that led to this work was made from data obtained mechanical properties testing and inspection testing, performance and quality control, performed in tubes made of polymer material, with or without molecular orientation. They were: Impact Resistance, Resistance Pressure Internal Hydro, Grade Gelling and resistance Methylene Chloride, Resistance Diametral compression, dimensional stability, Class of stiffness and resistance to flattening, resistance to extension of the fissure and Molecular Orientation degree. To obtain the data, the materials have been tested in real and extreme operating conditions, systems, equipment, instruments, “software” and accessories specified, assembled and calibrated in laboratory and manufacturing facilities, as technical regulations. For data records were used computer accessories systems for equipment, as well as spreadsheets and statistical and descriptive control “software” for parameter setting and mechanical tests. The data and results were analyzed according to parameters and dimensional stability criteria, toughness and rigidity, resistance to internal hydrostatic pressure, impact, methylene chloride, diametral compression and extension cleft associated to the degree of molecular orientation, based in technical bibliographies and rules regarding analyzes, testing and materials used. These criteria cover the design, calculation and parameters comparison, when the material applied to the pipe design. The effects resulting from the molecular orientation in the final mechanical properties of finished products. It was observed that the molecular orientation process provided the material greater toughness, greater resistance to the transmission of the crack, as well as higher resistance to fatigue, impact, tensile, compression and creep, higher modulus, and thus reduce safety coefficients applied to project.

京都大学 / 0048 / 新制・課程博士 / 博士(理学) / 甲第20657号 / 理博第4322号 / 新制||理||1621(附属図書館) / 京都大学大学院理学研究科化学専攻 / (主査)教授 寺西 利治, 教授 島川 祐一, 教授 小野 輝男 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DGAM

Filmes ultrafinos de polímeros que contém azocromóforos são importantes para muitas aplicações como armazenamento óptico, formação de grades de relevo superficiais, alinhamento de camadas de cristal líquido e dispositivos ópticos com propriedades não-lineares. Dentre as muitas técnicas de fabricação de filmes orgânicos ultrafinos, a técnica de Automontagem eletrostática camada a camada (Layer-by-Layer, LBL) é muito atrativa devido a sua simplicidade e versatilidade, permitindo o controle na espessura e na composição dos filmes em escalas nanométricas. Contudo, a completa caracterização estrutural de tais filmes enfrenta dificuldades devido à falta de técnicas experimentais apropriadas. Utilizamos a Geração de Segundo Harmônico (SHG) para estudar a orientação molecular de filmes automontados de um polieletrólito catiônico (PAH - Poli(alilamina hidroclorada)) e um polieletrólito aniônico contendo azocromóforos como grupos laterais (Ma-co-DR13) sobre substrato de vidro. O sinal de SHG é proporcional à susceptibilidade não-linear de segunda ordem do filme, que por sua vez depende da distribuição orientacional dos azocromóforos nesse filme. Os resultados indicam que existem uma orientação preferencial dos azocromóforos, que leva a uma não-linearidade óptica significativa. Entretanto, a intensidade do sinal e a anisotropia não são homogêneas por toda a amostra, indicando a presença de domínios orientacionais, que é verificado por meio da Microscopia a Ângulo de Brewster (BAM). O sinal médio de SHG não aumenta com a espessura do filme, indicando que a ordem orientacional das sucessivas bicamadas são independentes. Analisando o sinal de SHG em função das polarizações de saída e entrada, alguns parâmetros da distribuição orientacional dos azocromóforos podem ser deduzidos. Ajustando as medidas de SHG a uma distribuição modelo concluímos que os cromóforos possuem uma certa distribuição angular com um ângulo médio em relação à superfície do plano de aproximadamente 40° e uma pequena anisotropia ao longo do plano do filme. Utilizamos também o Método da Máxima Entropia (MEM) para determinar a distribuição mais larga possível compatível com nossos dados experimentais e comparar então com a distribuição modelo obtida através dos procedimentos de ajuste. / Ultrathin films of polymers containing azochromophores are important for many applications such as optical data storage, formation of surface relief gratings, liquid crystal alignment layers and non-linear optical devices. Among several techniques for fabricating organic thin films, the Layer-By-Layer electrostatic self-assembly (LBL) is very attractive due to its simplicity and versatility, allowing one to control film thickness and composition in the nanometer scale. However, thorough structural characterization of such films is often difficult due to lack of appropriate experimental techniques. We have used optical second-harmonic generation (SHG) to study the molecular orientation of Layer-by-Layer films of a cationic polyelectrolyte ((PAH - Poly(allylamine hydrochloride)) and a anionic polyelectrolyte containing azochromophores with azo side groups (PAH/Ma-co-DR13) on a glass substrate. The SHG signal is proportional to the second-order nonlinear susceptibility of the film, which in turn depends on the orientational distribution of the azo chromophores in the film. The results indicate that there is a preferential orientation of the azo chromophores in the film, leading to a significant optical nonlinearity. However, both the signal strength and its anisotropy are not homogeneous throughout the sample, indicating the presence of orientational domains. This is verified through Brewster Angle Microscopy (BAM). The average SHG signal does not increase with film thickness, indicating that the orientational order of successive bilayers are independent. Analyzing the SHG signal as a function of the input and output polarizations, a few parameters of the azochromophore orientational distribution can be deduced. Fitting the SHG signal to a simple model distribution, we have concluded that the chromophores have an angular distribution with a mean tilt from the surface plane of approximately 41° and a slight in-plane anisotropy. We have also used the Maximum-Entropy Method (MEM) to determine the widest orientational distribution compatible with our data and compared it to the model distribution obtained by the fitting procedure.

Filmes ultrafinos de polímeros que contém azocromóforos são importantes para muitas aplicações como armazenamento óptico, formação de grades de relevo superficiais, alinhamento de camadas de cristal líquido e dispositivos ópticos com propriedades não-lineares. Dentre as muitas técnicas de fabricação de filmes orgânicos ultrafinos, a técnica de Automontagem eletrostática camada a camada (Layer-by-Layer, LBL) é muito atrativa devido a sua simplicidade e versatilidade, permitindo o controle na espessura e na composição dos filmes em escalas nanométricas. Contudo, a completa caracterização estrutural de tais filmes enfrenta dificuldades devido à falta de técnicas experimentais apropriadas. Utilizamos a Geração de Segundo Harmônico (SHG) para estudar a orientação molecular de filmes automontados de um polieletrólito catiônico (PAH - Poli(alilamina hidroclorada)) e um polieletrólito aniônico contendo azocromóforos como grupos laterais (Ma-co-DR13) sobre substrato de vidro. O sinal de SHG é proporcional à susceptibilidade não-linear de segunda ordem do filme, que por sua vez depende da distribuição orientacional dos azocromóforos nesse filme. Os resultados indicam que existem uma orientação preferencial dos azocromóforos, que leva a uma não-linearidade óptica significativa. Entretanto, a intensidade do sinal e a anisotropia não são homogêneas por toda a amostra, indicando a presença de domínios orientacionais, que é verificado por meio da Microscopia a Ângulo de Brewster (BAM). O sinal médio de SHG não aumenta com a espessura do filme, indicando que a ordem orientacional das sucessivas bicamadas são independentes. Analisando o sinal de SHG em função das polarizações de saída e entrada, alguns parâmetros da distribuição orientacional dos azocromóforos podem ser deduzidos. Ajustando as medidas de SHG a uma distribuição modelo concluímos que os cromóforos possuem uma certa distribuição angular com um ângulo médio em relação à superfície do plano de aproximadamente 40° e uma pequena anisotropia ao longo do plano do filme. Utilizamos também o Método da Máxima Entropia (MEM) para determinar a distribuição mais larga possível compatível com nossos dados experimentais e comparar então com a distribuição modelo obtida através dos procedimentos de ajuste. / Ultrathin films of polymers containing azochromophores are important for many applications such as optical data storage, formation of surface relief gratings, liquid crystal alignment layers and non-linear optical devices. Among several techniques for fabricating organic thin films, the Layer-By-Layer electrostatic self-assembly (LBL) is very attractive due to its simplicity and versatility, allowing one to control film thickness and composition in the nanometer scale. However, thorough structural characterization of such films is often difficult due to lack of appropriate experimental techniques. We have used optical second-harmonic generation (SHG) to study the molecular orientation of Layer-by-Layer films of a cationic polyelectrolyte ((PAH - Poly(allylamine hydrochloride)) and a anionic polyelectrolyte containing azochromophores with azo side groups (PAH/Ma-co-DR13) on a glass substrate. The SHG signal is proportional to the second-order nonlinear susceptibility of the film, which in turn depends on the orientational distribution of the azo chromophores in the film. The results indicate that there is a preferential orientation of the azo chromophores in the film, leading to a significant optical nonlinearity. However, both the signal strength and its anisotropy are not homogeneous throughout the sample, indicating the presence of orientational domains. This is verified through Brewster Angle Microscopy (BAM). The average SHG signal does not increase with film thickness, indicating that the orientational order of successive bilayers are independent. Analyzing the SHG signal as a function of the input and output polarizations, a few parameters of the azochromophore orientational distribution can be deduced. Fitting the SHG signal to a simple model distribution, we have concluded that the chromophores have an angular distribution with a mean tilt from the surface plane of approximately 41° and a slight in-plane anisotropy. We have also used the Maximum-Entropy Method (MEM) to determine the widest orientational distribution compatible with our data and compared it to the model distribution obtained by the fitting procedure.

The present thesis investigates the electronic and structural properties of adenine, cytosine, and guanine layers on hydrogen passivated silicon (111)(7x7). The (7x7) reconstruction of the silicon surface was achieved by direct current heating of the samples in UHV conditions. After in situ hydrogen passivation layers of the DNA bases were prepared in different thicknesses by means of organic molecular beam deposition, all samples were characterized employing valence band and core level photoemission spectroscopy. Additionally the near edge x-ray absorption fine structure of the DNA base layers was investigated. A detailed and consistent picture of structural and electronic properties of the nucleotide bases in the solid state could be developed by comparison of measurements and DFT/B3LYP calculations.

L’électrofilage est une technique de mise en œuvre efficace et versatile qui permet la production de fibres continues d’un diamètre typique de quelques centaines de nanomètres à partir de l’application d’un haut voltage sur une solution concentrée de polymères enchevêtrés. L’évaporation extrêmement rapide du solvant et les forces d’élongation impliquées dans la formation de ces fibres leur confèrent des propriétés hors du commun et très intéressantes pour plusieurs types d’applications, mais dont on commence seulement à effleurer la surface. À cause de leur petite taille, ces matériaux ont longtemps été étudiés uniquement sous forme d’amas de milliers de fibres avec les techniques conventionnelles telles que la spectroscopie infrarouge ou la diffraction des rayons X. Nos connaissances de leur comportement proviennent donc toujours de la convolution des propriétés de l’amas de fibres et des caractéristiques spécifiques de chacune des fibres qui le compose. Les études récentes à l’échelle de la fibre individuelle ont mis en lumière des comportements inhabituels, particulièrement l’augmentation exponentielle du module avec la réduction du diamètre. L’orientation et, de manière plus générale, la structure moléculaire des fibres sont susceptibles d’être à l'origine de ces propriétés, mais d’une manière encore incomprise. L’établissement de relations structure/propriétés claires et l’identification des paramètres qui les influencent représentent des défis d’importance capitale en vue de tirer profit des caractéristiques très particulières des fibres électrofilées. Pour ce faire, il est nécessaire de développer des méthodes plus accessibles et permettant des analyses structurales rapides et approfondies sur une grande quantité de fibres individuelles présentant une large gamme de diamètre. Dans cette thèse, la spectroscopie Raman confocale est utilisée pour l’étude des caractéristiques structurales, telles que l’orientation moléculaire, la cristallinité et le désenchevêtrement, de fibres électrofilées individuelles. En premier lieu, une nouvelle méthodologie de quantification de l’orientation moléculaire par spectroscopie Raman est développée théoriquement dans le but de réduire la complexité expérimentale de la mesure, d’étendre la gamme de matériaux pour lesquels ces analyses sont possibles et d’éliminer les risques d’erreurs par rapport à la méthode conventionnelle. La validité et la portée de cette nouvelle méthode, appelée MPD, est ensuite démontrée expérimentalement. Par la suite, une méthodologie efficace permettant l’étude de caractéristiques structurales à l’échelle de la fibre individuelle par spectroscopie Raman est présentée en utilisant le poly(éthylène téréphtalate) comme système modèle. Les limites de la technique sont exposées et des stratégies expérimentales pour les contourner sont mises de l’avant. Les résultats révèlent une grande variabilité de l'orientation et de la conformation d'une fibre à l'autre, alors que le taux de cristallinité demeure systématiquement faible, démontrant l'importance et la pertinence des études statistiques de fibres individuelles. La présence de chaînes montrant un degré d’enchevêtrement plus faible dans les fibres électrofilées que dans la masse est ensuite démontrée expérimentalement pour la première fois par spectroscopie infrarouge sur des amas de fibres de polystyrène. Les conditions d'électrofilage favorisant ce phénomène structural, qui est soupçonné d’influencer grandement les propriétés des fibres, sont identifiées. Finalement, l’ensemble des méthodologies développées sont appliquées sur des fibres individuelles de polystyrène pour l’étude approfondie de l’orientation et du désenchevêtrement sur une large gamme de diamètres et pour une grande quantité de fibres. Cette dernière étude permet l’établissement de la première relation structure/propriétés de ces matériaux, à l’échelle individuelle, en montrant clairement le lien entre l’orientation moléculaire, le désenchevêtrement et le module d'élasticité des fibres. / Electrospinning is an efficient and versatile technique to produce continuous fibers of typical diameter of a few hundred nanometers from the application of a high voltage on a concentrated and entangled polymer solution. The rapid solvent evaporation and the significant elongational forces involved in the fiber formation process give rise to unusual properties that are interesting for various types of applications, but that are yet to be fully explored. Due to their small size, these materials have been, for a long time, studied into bundles composed of thousands of fibers using conventional techniques such as infrared spectroscopy and X-ray diffraction. Our current understanding of their behavior thus relies on a convolution of the properties of the mat and the specific characteristics of each fiber composing it. Recent studies at the individual fiber level have revealed unusual properties, particularly an exponential increase of the modulus with the diameter reduction. The orientation and the molecular structure within the fibers are suspected to be at the origin of these properties, but in a way that is still far from being understood. Establishing clear structure/properties relationships and identifying the parameters that influence them represent significant challenges. However, they are of tremendous importance to fully take advantage of the specific characteristics of electrospun fibers. A key step toward this goal is to develop methodologies that enable fast and in-depth structural analysis on large quantities of individual fibers with a large diameter range. In this thesis, confocal Raman spectroscopy is used to probe structural characteristics of individual fibers such as their molecular orientation, crystallinity and disentanglement. A new methodology for orientation quantification is first demonstrated theoretically with the objectives of reducing the experimental complexity of the Raman measurements, of extending the variety of materials that can be analysed, and of eliminating recurrent errors brought by the use of the conventional method. The experimental validity and applicability of this new method, referred to as MDP, is then demonstrated. Following this, an efficient protocol enabling the structural study of individual electrospun fibers by confocal Raman spectroscopy is presented, using poly(ethylene therephthalate) as a model system. The limitations of the technique are exposed and experimental strategies to circumvent them are highlighted. Results reveal the large variability of the orientation and of chain conformation from fiber to fiber, showing the importance and the relevance of statistical studies of individual fibers. Following this, the presence of chains showing a level of entanglement lower in electrospun fibers than in the bulk is demonstrated experimentally for the first time using infrared spectroscopy on bundles of polystyrene fibers. The principal electrospinning conditions promoting this structural phenomenon, which is suspected to influence greatly the properties of the fibers, are identified. Finally, the various methodologies developed in the thesis are combined for an in-depth study of orientation and disentanglement on large quantities of individual polystyrene fibers covering a large diameter range. This last study enables establishing the first structure/properties relationships for these materials, at the individual fiber scale, by clearly exposing the link between orientation, disentanglement and the elastic modulus of the fibers.

The goal of this research is to investigate the combined effects of glass fibre reinforcement and molecular orientation in polypropylene-short glass fibre composites. Specimens have been fabricated using the injection moulding process and drawn using a small die drawing rig. The effects of die drawing on the fibre composites are complex, with the drawing process orienting both the polymer molecules and the glass fibres. This may be accompanied by the creation of voids in the polymer matrix and their destruction in the compressive stress field thus restoring the interfacial contact area between fibre and matrix. Unfilled and short glass fibre filled polypropylene specimens, with fibre content 7% wt, 13%wt, 27%wt, and 55%wt, were injection moulded prior to the die drawing process. An experimental program of die drawing within an oven at elevated temperature was conducted for polypropylene filled to various levels and at different strain rates. The specimens drew to draw ratios in the range γ=1.41 to γ=5.6. Mechanical characterization of the test materials has been conducted by examining the tensile stress strain and fracture behaviour under uniaxial conditions. The influence of glass fibre content and drawing conditions (draw ratio) on the fracture toughness and crack propagation was investigated using the double edge notched fracture test. The notch lengths ranged from 1.5 to 2.5 mm for 10 mm wide specimens. The critical stress intensity factor increased as the fibre content increased up to a limiting filler level. The fracture toughness of both unfilled and fibre filled polypropylene were found to be highly dependent on draw ratio. The results were analysed to find out the optimal draw ratio and fibre content that yielded the maximum modulus, strength and fracture toughness. Data showed that, at a given draw ratio, modulus, strength and fracture toughness increased with increasing fibre content to a maximum and then decreased. The optimum material was obtained at a draw ratio of 2.5 and filler loading 13wt%.

In dieser Arbeit wurde die Austrittsarbeit von Graphen, einer vielversprechenden Elektrodenmaterial für (opto)- elektronische Bauteile, durch die Adsorption von luftbeständigen konjugierten organischen Molekülen (KOMs), welche als Akzeptoren und Donatoren fungieren, modifiziert. Die Eigenschaften der Valenz- und Rumpfniveaus sowie die Austrittsarbeitsmodifikation der vakuumverdampften KOMs wurden mit Photoelektronenspektroskopie (PES) untersucht, während die Orientierung der KOMs mit Röntgen-Nahkanten-Absorptions-Spektroskopie (NEXAFS) aufgeklärt wurde. Die Austrittsarbeit von Graphen auf Quartz (G/Qu) lässt sich auf maximal 5.7 eV und minimal 3 eV anpassen, welches aus einem Ladungstransfer direkt an der Grenzfläche resultiert, der keine Ausbildung von kovalenten Bindungen zwischen der molekularen Monolage und dem Graphen beinhaltet. Zudem, für den starken molekularen Akzeptor Hexaazatriphenylen-Hexacarbonitril (HATCN) verläuft die Austrittsarbeitserhöhung über eine Orientierungsänderung der Moleküle im Monolagenbereich. Für alle anderen auf G/Qu abgeschiedenen Akzeptoren (Donatoren) wurde beobachtet, dass der Ladungstransfer eine positive (negative) Oberflächen-ladungsdotierung der Graphen-Schicht bewirkt, welches in einer Austrittsarbeitserhöhung (-erniedrigung) resultiert. Letztere ließ sich jeweils in zwei Beiträge zerlegen: (a) Verschiebung des Vakuumniveaus durch einen Grenzflächendipol an der KOM/Graphen-Grenzfläche und (b) Verschiebung des Fermi-Niveaus durch Oberflächenladungstransferdotierung der Graphen-Schicht. Weiterhin wurde der molekulare Akzeptor Hexafluoro-tetracyano napththoquinodimethan (F6TCNNQ) sowohl auf G/Qu als auch auf Graphen auf Kupfer abgeschieden, wobei sich herausstellte, dass der Ladungstransfer im ersteren Fall vom Graphen stammt, und im letzteren von der Kupferunterlage. Die Ergebnisse werden von Dichtefunktionaltheorieberechnungen gestützt und tragen erheblich zum Verständnis von Graphen/KOM-Grenzflächen bei. / In this thesis, the work function of graphene, a promising electrode for (opto)electronic devices was modified by adsorption of air-stable conjugated organic molecules (COMs) that act as strong molecular acceptors or donors. The valence and core level properties, together with the work function modification of the vacuum-deposited COMs on graphene were investigated with photoelectron spectroscopy (PES), while the orientation of COMs was studied with near edge X-ray fine structure spectroscopy (NEXAFS). The work function of graphene-on-quartz (G/Qu) is modified up to 5.7 eV and down to 3 eV as a result of charge transfer (CT) occurring right at the interface, which does not invoke covalent bond formation between the molecular monolayer and the graphene. In addition to the CT, in the case of the molecular acceptor hexaazatriphenylene-hexacarbonitrile (HATCN), the work function increase proceeded via a density-dependent re-orientation of the molecule in the monolayer regime. For all the other tested molecular acceptors (donors) deposited on graphene-on-quartz, the CT was observed to induce positive (negative) surface CT doping of the graphene layer, leading to a work function increase (decrease) and was disentangled into two contributions: (a) shift of the Vacuum level due to the formation of an interface dipole at the COM/graphene interface and (b) shift of the Fermi level of the graphene due to the surface CT doping. Additionally, the molecular acceptor hexafluoro-tetracyanonapththoquinodimethane (F6TCNNQ) was deposited on both G/Qu and graphene-on-copper, where the CT was found to originate from graphene and copper support respectively. The findings were supported by density functional theory calculations and significantly add to a fundamental understanding of graphene/COM interfaces.

In dieser Arbeit werden Fragestellungen aus dem Gebiet der Organischen Elektronik behandelt, hauptsächlich Grenzflächen zwischen Metallen und konjugierten organischen Molekülen (KOM). Im einzelnen wird behandelt: (i) der Einfluss der Orientierung von Molekülen auf die Energieniveaus, (ii) das gezielte Einstellen von Energieniveaus mithilfe starker Elektronenakzeptoren, (iii) die Rolle des thermodynamischen Gleichgewichts an organisch-organischen Grenzflächen und (iv) der Zusammenhang zwischen elektronischer Struktur an Grenzflächen und dem Bindungsabstand. Es wurden hauptsächlich Messungen mit ultravioletter Photoelektronenspektroskopie, unterstützt von Röntgenphotoelektronenspektroskopie, Spektroskopie mit metastabilen Atomen, Röntgenbeugung und stehenden Röntgenwellen, an vakuumsublimierten organischen dünnen Schichten im Ultrahochvakuum durchgeführt. (i) Eine neue Erklärung für das Phänomen der orientierungsabhängigen Ionisationsenergie in molekularen Verbünden wird gegeben. Dabei kommt es zu einem Einfluss intramolekularer Dipole auf die Ionisationsenergie. (ii) Es wurde eine neue Methode gefunden, um die Lochinjektionsbarriere (HIB) an organisch/metallischen Grenzflächen zu kontrollieren. Dazu wurden (Sub-)Monolagen starker Elektronenakzeptoren auf Metalloberflächen adsorbiert. Dabei kommt es zu einem Ladungstransfer, der die HIB eines darauf aufgedampften KOMs verringern kann. Das Konzept wurde mit drei Akzeptoren getestet und die HIB konnte um bis zu 1,2 eV verringert werden. (iii) Ein akzeptorvorbedeckungsabhängiger Übergang von Vakuumniveauangleichung zu einem „Pinning“ molekularer Niveaus an Homogrenzflächen eines KOMs mit liegender Mono- und stehender Multilage konnte beobachtet werden - ein direkter Beweis für einen thermodynamisch getriebenen Ladungstransfer. (iv) Ein klarer Zusammenhang zwischen der Stärke der chemischen Bindung und dem Bindungsabstand von KOM zu Metallsubstraten konnte gezeigt werden. / This work addresses several topics of the field of organic electronics, the focus lies on organic/metal interfaces. Four main topics have been covered: (i) the impact of molecular orientation on the energy levels, (ii) energy level tuning with strong electron acceptors, (iii) the role of thermodynamic equilibrium at organic/organic homo-interfaces and (iv) the correlation of interfacial electronic structure and bonding distance. To address these issues mainly ultraviolet photoelectron spectroscopy was used, supported by X-ray photoelectron spectroscopy, metastable atom electron spectroscopy, X-ray diffraction and X-ray standing waves, to examine vacuum sublimed thin films of conjugated organic molecules (COMs) in ultrahigh vacuum. (i) A novel approach is presented to explain the phenomenon that the ionization energy in molecular assemblies is orientation dependent. It is demonstrated that this is due to an impact of intramolecular dipoles on the ionization energy in molecular assemblies. Furthermore, the correlation of molecular orientation and conformation has been studied in detail for COMs on various substrates. (ii) A new approach was developed to tune hole injection barriers (HIB) at organic/metal interfaces by adsorbing a (sub-) monolayer of an organic electron acceptor on the metal electrode. Charge transfer from the metal to the acceptor leads to a chemisorbed layer, which reduces the HIB to the COM overlayer. With this concept a lowering of the HIB of up to 1.2 eV could be observed. (iii) A transition from vacuum-level alignment to molecular level pinning at the homo-interface between a lying monolayer and standing multilayers of a COM was observed, which depended on the amount of a pre-deposited acceptor. (iv) A clear correlation between the strength of chemical bonding of COMs and the bonding distance to metal substrates could be shown.